The U.S. is suffering through the worst drought since the 1950s. It's especially hurt farmers, who are desperately searching for new sources of water. And they think they've found the perfect solution.

It's groundwater stored in aquifers. The temptation to use this water is irresistible. It seems like it's everywhere and it's mostly unregulated. The problem is, it's also finite.

Think of an aquifer as a giant milkshake glass and each well as a straw in the glass. Most states allow an unlimited number of straws. This situation is sustainable only if the amount of water sucked out doesn't exceed the amount that is replenished by rainwater.

But, the laws governing groundwater are encouraging a race to the bottom of the glass. Many states apply what is called the "reasonable use" doctrine. This allows landowners to pump an unlimited amount of water for whatever they deem a "beneficial use."

It used to be that only Western farmers pumped groundwater to irrigate crops. Now, it's happening across the country.

The cumulative effect of this change has profound implications for the country's water supplies because irrigation uses more water than anything else.

States are struggling to find water for farms, cities and industry. And they should establish sensible restrictions on the drilling of new wells and on the quantity pumped from existing ones.

Defenders of unrestricted groundwater pumping insist that landowners have a property right to the groundwater beneath their land. But adjoining landowners share the same "right."

Unlimited pumping is like a circular firing squad. It guarantees mutually assured destruction. Or in this case, mutually assured depletion of a precious resource.